Giant Hogweed (Heracleummantegazzianum) - PoisonousInvader of the Northeast NYSG Invasive Species Factsheet Series: 07-1Charles R. O’Neill, Jr.Invasive Species SpecialistNew York Sea GrantFebruary 2007, Revised August 2009

New York’s Sea Grant Extension Program

provides Equal Program and Equal Employment

Opportunities in associa-tion with Cornell Coop-erative Extension, U.S.

Department of Agriculture and U.S. Department of

Commerce, and cooperat-ing County Cooperative Extension Associations.

New York Sea GrantSUNY College at

BrockportBrockport, NY 14420Tel: (585) 395-2638Fax: (585) 395-2466

Heracleum

mantegazzianum

Should you be walking along a damp abandoned railroad right-of-way, a wet roadside ditch or a stream bank and stumble upon a plant that looks like Queen Anne’s Lace with an attitude – more than 10 feet tall with two-inch thick stems, flowers two or more feet across and leaf clusters as wide as you can stretch your arms – stay clear! You have just become one of an increasing number of New Yorkers who have met the state’s most striking, and dangerous, invasive plant, the giant hogweed (Heracleum mantegazzianum) and you absolutely do not want to touch it and take it home to the family. Giant hogweed can make a case of poison ivy seem like a mild itch.

Photo: Randy Westbrooks, USGS

Introduction

History and Distribution

A member of the carrot and parsley family of plants (Apiaceae), giant hogweed is native to the Caucasus region of Eurasia. Because of its unique size and impressive flower head, the plant was originally introduced to Great Britain as an ornamental curiosity in the 19th century. The plant is named after the mythological god, Hercules (he of robust size and strength). It was later transported to the United States and Canada as a showpiece in arboreta and Victorian gardens (one of the plant’s first North American plantings of giant hogweed was in gardens near Highland Park in the City of Rochester, New York). It was also a favorite of beekeepers because of the size its flower heads (the amount of food for bees is substantial). A powder made from the dried seeds is also used as a spice in Iranian cooking. Unfortunately, as with so many invasive plants, giant hogweed escaped cultivation and has now become naturalized in a number of areas, including: Broome, Cattaraugus, Cayuga, Chautauqua, Erie, Genesee, Herkimer, Jefferson, Lewis, Livingston, Madison, Monroe, Nassau, Niagara, Oneida, Onondaga, Ontario, Orange, Orleans, Oswego, Putnam, Schuyler, Steuben, Sullivan, Tioga, Tompkins, Wayne, Wyoming, and Yates Counties in New York; Connecticut; the

Giant hogweed (Heracleum mantegazzianum) is a member of the carrot or parsley family, Apiaceae (Umbelliferae). Except for its size, the plant can be mistaken for a number of native, noninvasive plants such as cow parsnip (Heracleum lanatum), Angelica (Angelica atropurpurea), and poison hemlock (Conium maculatum). Of these, the plant most likely to be misidentified as giant hogweed is cow parsnip. A fourth, not so innocuous, invasive giant hogweed imposter found throughout North America is wild parsnip (Pastinaca sativa). Information on how to distinguish these giant hogweed wannabees from the real thing can be found later in this factsheet.

Giant hogweed is a perennial herb with tuberous root stalks. It survives from one growing season to another by forming perennating buds (surviving from season to season) and enduring a period of dormancy during the winter. The plant develops numerous white flowers that form a flat-topped, umbrella-shaped head up to two and a half feet across, resembling “Queen Anne’s Lace on steroids.” Flowers form from late-spring through mid-summer. Numerous (up to 100,000), half inch long, winged, flattened oval seeds form in late-summer. These seeds, originally green, turn brown as they dry and can be spread by animals, surface runoff of rain, or on the wind, establishing new colonies. Seeds can remain viable in the soil for up to 10 years. The plant’s stems die in the fall and remain standing through the winter, topped with the huge, brown dead flower heads.

Giant hogweed’s thick hollow stems are generally one to three inches in diameter but can reach four inches. Also impressive are the plant’s lobed, deeply incised compound leaves, which can reach up to five feet in width. The plant may grow to 15 to 20 feet in height.

Giant hogweed can colonize a wide range of habitats but prefers rich, damp soil such as that found along abandoned railroad rights-of-way, roadside ditches, stream banks, or other moist disturbed areas. Because of this predilection for wet areas, the plant is considered to be an aquatic invasive species.2

Confirmed sightings - August 2009

District of Columbia; Illinois; Maine; Maryland; Massachusetts; Michigan; Ohio; Oregon; Pennsylvania; Washington; Wisconsin; and the Canadian Provinces of British Columbia, New Brunswick, Ontario and Quebec.

Because of its public health hazard potential and, to a lesser extent, to its potential ecological impacts, giant hogweed is on the federal noxious weed list and several state lists of prohibited plant species.

Biology and Habitat

Photo: Terry English, USDA APHIS PPQ

Giant hogweed leaves can be up to five feet across.Photo: Thomas B. Denholm, NJDA

3

IDENTIFICIDENTIFICIDENTIFICIDENTIFICIDENTIFICAAAAATIONTIONTIONTIONTION

As mentioned earlier, there are several plants in New York and the Northeast that can be mistaken for gianthogweed. Key features for distinguishing these plants from giant hogweed are explained below.Comparisson photographs can be found in tables on pages 4 and 5.

Giant hogwGiant hogwGiant hogwGiant hogwGiant hogweedeedeedeedeed may grow to 15 to 20 feet in height. Stems are 1 to 3 inches in diameter, but may reach 4inches. Stems are marked with dark purplish blotches and raised nodules. Leaf stalks are spotted, hollow,and covered with sturdy bristles (most prominent at the base of the stalk). Stems are also covered withhairs but not as prominently as the leaf stalks. Leaves are compound, lobed, and deeply incised; can reachup to 5 feet in width. Numerous white flowers form a flat-topped, umbrella-shaped head up to two and ahalf feet across. [Photos, page 4]

Native CoCoCoCoCow parw parw parw parw parsnipsnipsnipsnipsnip, while resembling giant hogweed, grows to only five to eight feet tall. The deeplyridged stems can be green or slightly purple, do not exhibit the dark purplish blotches and raised nodulesof hogweed, and only reach one to two inches in diameter, contrasted with hogweed stems which canreach three to four inches in diameter. Where giant hogweed has coarse bristly hairs on its stems andstalks, cow parsnip is covered with finer hairs that give the plant a fuzzy appearance. Both sides of theleaves exhibit these hairs but they are predominantly on the underside of the leaves. In contrast tohogweed’s two to two and a half foot flower heads, cow parsnip flower clusters are less than a foot across.The size difference carries over into leaf size with hogweed’s five foot, deeply incised leaves replaced byleaves that are less incised and only two to two and a half foot across. [Photos, page 4]

Native purpurpurpurpurple-stple-stple-stple-stple-stemmed Angelicaemmed Angelicaemmed Angelicaemmed Angelicaemmed Angelica is more easily differentiated from giant hogweed by its smooth, waxygreen to purple stems (no bristles, no nodules), and its softball-sized clusters of greenish-white or whiteflowers, seldom reaching a foot across. As with cow parsnip, Angelica is much shorter than gianthogweed, usually no more than eight feet tall. Angelica leaves are comprised of many small leaflets andseldom reach more than two feet across. [Photos, page 4]

PPPPPoison hemlocoison hemlocoison hemlocoison hemlocoison hemlockkkkk, a non-native biennial, is also shorter than giant hogweed, growing to only four to ninefeet in height. While the stem has some purple blotches, it is waxy and the entire plant (stems, stalks,leaves) is smooth and hairless. The leaves are dramatically different from those of hogweed, being fern-like and a bright, almost glossy, green. All branches have small flat-topped clusters of small white flowers.Another distinguishing characteristic is poison hemlock’s unpleasant mouse-like odor. The entire plant istoxic, and the volatile alkaloids can even be toxic when inhaled. [Photos, page 5]

Wild parWild parWild parWild parWild parsnipsnipsnipsnipsnip, like giant hogweed, is of special concern because it, too, can cause phytophotodermititis,only not usually as severe as that of giant hogweed. This plant can be found extensively throughout NY’sSouthern Tier, in the region east of Lake Ontario, some Central and Western NY counties, parts of theCatskills and counties east of the Hudson River. Unlike the perennial giant hogweed, wild parsnip is abiennial, producing a rosette of leaves close to the ground in its first year and a single flower stalk with aflat-topped umbel with clusters of yellow flowers in its second year. The plant reproduces by means of theseeds of these flowers; it does not regrow from its root as does giant hogweed. Wild parsnip is muchsmaller than giant hogweed, seldom exceeding 5-feet in height. Wild parsnip stems are yellowish-greenwith verticle grooves running their length. Wild parsnip has compound pinnate leaves with 5 to 15 toothedand variably lobed yellowish-green leaves. [Photos, page 5]

IMPIMPIMPIMPIMPAAAAACTCTCTCTCTSSSSS

Giant hogweed is one of a very few North American invasive plants that can cause human health impactsas well as ecological damage.

4

DEEWGOHTNAIG

THGIEH

teef02ot51

METSretemaidhcni3ot1ffits,sehctolbelpruP

seltsirb

FAEL,debol,dnuopmoCotpu;desicniylpeed

ediwteef5

REWOLF-talf,srewolfetihWpu,allerbmu,deppot

ssorcateef5.2ot

PINSRAPWOC

THGIEH

teef8ot5

METSretemaidhcni2ot1neerg,degdirylpeeDenif,elprupylthgilsot

yzzuf,sriah

FAELssel,dnuopmoC

teef2/12ot2,desicnisriahyzzuf,ssorca

REWOLFsretsulcrewolfhsitihW

toof1nahtregralonssorca

ACILEGNA

THGIEH

teef9ot4

METSneergyxaw,htoomS

,)seltsirbon(elprupothcni2/12ot1

retemaid

FAEL,stelfaelllamsynaMowtnahterommodles

ssorcateef

REWOLF,sretsulcdezis-llabtfoS

roetihw-hsineergtoof1otpu,etihw

ssorca

5

KCOLMEHNOSIOP

THGIEH

teef9ot4

METS,sselriahdnahtoomS

emos,neergyxawot1,sehctolpselprup

retemaidhcni2

FAEL,thgirb,ekil-nreF

neerg,yssolgtsomla

REWOLFevahsehcnarbllA

deppot-talfllamsetihwllamsfosretsulc

srewolf

PINSRAPDLIW

THGIEH

teef5otpU

METShtiwneerg-hsiwolleY

sevoorgelcitrevhtgnelllufgninnur

FAEL5,etannip,dnuopmoCylbairav,dehtoot51otneerg-hsiwolley,debol

REWOLFklatsrewolfelgniS

lebmudeppot-talfhtiwwolleyderetsulcfo

srewolf

Ecological ImpactsEcological ImpactsEcological ImpactsEcological ImpactsEcological Impacts

Colonies of giant hogweed can become quite dense owing to the plant’s prolific seed production andrapid growth rate. Such dense stands crowd out slower growing plants, the thick hogweed canopydisplacing native plants that need direct sunlight to grow. The decreased abundance of beneficial nativeplants can reduce the utility of the area for wildlife habitat. When riparian plants are displaced, streambank erosion can increase and streambeds can be covered with silt.

Human Health ImpactsHuman Health ImpactsHuman Health ImpactsHuman Health ImpactsHuman Health Impacts

Giant hogweed is one of a handful of plants in the Northeast that can cause a significant reaction whenhumans come in direct contact with the plant. Spread of this plant in urban and suburban areas is viewedas an incipient public health hazard. [Wild parsnip can result in almost as severe reactions.]

Soon after humans bruise the leaves or stems of the more common poison ivy, poison oak, and poisonsumac, an allergic reaction to the plants’ poisonous oil (akin to carbolic acid) causes significant skin

6

irritation, itching, rashes and open sores. In the case of giant hogweed, however, the skin inflammationis not caused by simply brushing against the plant’s leaves or stems. For giant hogweed to affect aperson, sap from a broken stem or crushed leaf, root, flower or seed must come into contact with moistskin (perspiration will suffice) with the skin then being exposed to sunlight. Irritation is not immediate,but will usually appear within one to three days after exposure. This form of skin irritation (dermatitis)is called “phytophotodermatitis”. The plant’s clear, watery sap contains a glucoside calledfuranocoumarin that is a psoralen. Psoralens sensitize the skin to ultraviolet radiation and can result insevere burns, blistering, painful sores, and purplish or blackened scars. These phototoxic effects are theresult of the binding of the psoralens to nuclear DNA under the influence of ultraviolet irradiation, andthe subsequent death of affected cells.

The first signs of giant hogweed-causedphotodermatitis are when the skin turns red andstarts itching. Within 24 hours, burn-like lesionsform, followed by large, fluid filled blisterswithin 48 hours. The initial irritation usually willsubside within a few days, but affected areas mayremain hypersensitive to ultraviolet light formany years and re-eruptions of lesions andblisters may occur. On rare occasions,particularly in very sensitive individuals, theburns and blisters may be bad enough to require

hospitalization. A side effect of exposure to the psoralens is the production of excessive amounts ofmelanin in the skin, resulting in residual brown blotches called hyper-pigmentation; scars and brown toblack blotches may last for several years. The worst risk of exposure to giant hogweed is to one's eyes -getting even minute amounts of the sap in the eyes can result in ttemporary or even permanentblindness. Medical help should be sought immediately; by the time symptoms of burning andhypersensitivity to sunlight are apparent, the damage could already be irreversible.

The only known antidote to contact with the sap is to immediately wash skin thoroughly with soap andwater, removing the sap and hopefully preventing any reaction with subsequent exposure to sunlight.Once the irritation begins, medical advice should be sought. Treatment with prescription topicalsteroids early on may reduce the severity of a person’s reaction. It will also be important to cover theburns and blisters with light sterile dressings to prevent infection. Long-term, use of sunblock insubsequent years may be required to prevent sensitization by sunlight again.

People most at risk include landscape technicians and yard maintenance laborers who may come incontact with the sap when cutting the plant down or using line trimmers to control new growth.Children breaking off the long, bamboo-like stems to use as play swords are also at great risk.However, sometimes direct contact with the plant is not necessary for a reaction. Farmers have beenknown to develop symptoms when they touch cows who have gotten the sap on their skin whilegrazing (cows, themselves, seem impervious to the sap). The best prevention measure is to wear longsleeves and long-legged pants when contact with the plant is a possibility.

CONTRCONTRCONTRCONTRCONTROLOLOLOLOL

If it weren’t for giant hogweed’s public health impacts, the plant most likely would not be worth theeffort of controlling it. Although it does have ecologic impacts, they are not as severe as many otherwetland invasive plants. However, the health impacts can be severe and the plant has found itself on thefederal noxious weed list and several state lists, as well. It is a particular target of parks and transporta-tion/highway departments’ invasive plant eradication efforts. Such eradication programs can incorpo-rate a combination of physical removal and chemical control. If undertaken properly, such programs canbe done without harm to humans or damage to the environment. Recently some landowners have been

USDA APHIS PPQ

7

known to refuse permission to allow highway departments to chemically treat giant hogweed thickets. It is believed that this is usually a case of lack of knowledge on the landowner’s part.

Giant hogweed is very difficult to eradicate. Although the stems, stalks, leaves and flowers can be killed with a number of common selective herbicides, such as 2,4-D (the third most-often used herbicide in North America), dicamba (a benzoic acid herbicide), TBA (terbuthylazine) and MCPA, these herbicides are not effective at killing the plant’s tuberous perennial roots. Another common, selective broadleaf herbicide, triclopyr (a common brand name is Brush-B-Gone®), is also effective, particularly when applied directly to the entire surface of leaves and stems during periods of active growth; numerous applications may be needed to kill the root stalk. Cornell Cooperative Extension recommends early application (during the bud stage and the period of active plant growth) of glyphosate (commonly sold under the trade names Rodeo® and Roundup®). Care should be taken when using any herbicides to control giant hogweed; particular care should be taken when using glyphosate as it is nonselective and will kill both the hogweed and desirable plants such as grass.

For those hesitant to utilize herbicides, giant hogweed can be managed using various “cultural” methods. Unfortunately, owing to the plant’s persistence and spread by blowing seeds, such control can take many seasons worth of effort to achieve 100% control. Individual plants can be dug out, removing the entire rootstalk, a difficult process, particularly in patches where the plant has spread by root growth. Mowing, cutting and use of line trimmers can be used to remove a standing crop and starve the rootstalk. Unfortunately, unless performed numerous times during a season, mowing only serves to stimulate budding on the rootstalk. All of these methods should be done with extreme care and only while wearing protective clothing and eye protection. Skin contact with soiled clothing should also be avoided. Biocontrol by grazing cows and pigs (which are apparently not affected by the plant’s sap) may also help to manage but not eliminate the plant. Care should be taken not to get sap on uncovered skin when touching livestock after the animals contact crushed or bruised hogweed.

Control of wild parsnip is less difficult than controlling giant hogweed because as a biennial, wild parsnip reproduces only from seed, not from its rootstock. This plant can be controlled by cutting the stem from the root below ground level with a shovel, spade or machete before the seed head matures.

And If All of That Isn’t Strange Enough…

Very few invasive species get immortalized in song. Giant hogweed is an exception. In 1971, Genesis released their album “Nursery Cryme” which includes the song “The Return of the Giant Hogweed.”

“Turn and run! Nothing can stop them,Around every river and canal their power is growing.Stamp them out! We must destroy them,They infiltrate each city with their thick dark warning odour.

Waste no time! They are approaching.Hurry now, we must protect ourselves and find some shelterStrike by night! They are defenseless.They all need the sun to photosensitize their venom.

They are invincible, They seem immune to all our herbicidal battering.”

If you find giant hogweed in NYS, you are encouraged to call NYS DEC’s Giant Hogweed Hotline:

845-256-3111

Her

acle

um m

ante

gazz

ianu

m

New York Sea GrantSUNY College at

BrockportBrockport, NY 14420Tel: (585) 395-2638Fax: (585) 395-2466

Produced by New York Sea Grant, February 2006

RRRRRefefefefeferenceserenceserenceserenceserences

Anon. Giant Hogweed (Heracleum mantegazzianum). Written Findings of the State Noxious WeedControl Board - Class A Weed. State of Washington. 4 pp.

Camm E, et al. 1976. Phytophotodermatitis from Heracleum mantegazzianum. Contact Dermatitis. 2,68-72.

Davies DHK, Richards MC. 1985. Evaluation of herbicides for control of giant hogweed (Heracleummantegazzianum Somm & Lev.), and vegetation re-growth in treated areas. Tests of Agrochemicals andCultivars. Annals of Applied Biology. (6):100-101.

Genesis. 1971. The Return of the Giant Hogweed.

Hypio, P, Cope, E. 1982. Giant Hogweed, Heracleum mantegazzianum. Cornell Cooperative Exten-sion. Misc. Bulletin 123.

Kees H, Krumrey G. 1983. Heracleum mantegazzianum - ornamental plant, weed and poisonous plant.[toxicity to livestock and humans, control]. Gesunde Pflanzen. Kommentator.3 5(4):108-110.

Northall F. 2003. Vegetation, Vegetables, Vesicles: Plants and Skin. Emerg. Nurse. 11(3):18-23.

InfInfInfInfInformational Linksormational Linksormational Linksormational Linksormational Links

Giant Hogweed - Overview, Invasive Plant Council of New York State: http://www.ipcnys.org/sections/target/giant_hogweed_overview.htm

Giant Hogweed (Heracleum mantegazzianum), Written Findings of the State Noxious Weed ControlBoard - Class A Weed: http://www.nwcb.wa.gov/weed_info/Written_findings/Heracleum_mantegazzianum.html

Potential Health Hazard, Giant Hogweed (Heracleum mantegazzianum). Allegany/Cattaraugus HomeGrounds & Gardens, Cornell Cooperative Extension: http://counties.cce.cornell.edu/allegany_cattaraugus/hort/PestAlert.htm

PhoPhoPhoPhoPhotttttograph and Graphics Creditsograph and Graphics Creditsograph and Graphics Creditsograph and Graphics Creditsograph and Graphics Credits

Page 1: Randy Westbrooks, U.S. Geological Survey, www.forestryimages.orgMap, page 2: New York Sea GrantPage 2, right: Terry English, USDA APHIS PPQ, www.forestryimages.orgPage 2, left: Thomas B. Denholm, New Jersey Department of Agriculture, www.forestryimages.orgPage 3: USDA APHIS PPQ, www.forestryimages.orgGiant Hogweed Table, left to right: Terry English, USDA APHIS PPQ @ www.forestryimages.org Cornell Cooperative Extension - Allegany/Cattaraugus Counties Donna R. Ellis, University of Connecticut @ www.forestryimages.org Terry English, USDA APHIS PPQ @ www.forestryimages.orgCow Parsnip Table, left to right: UMASS Extension @ http://www.umassgreeninfo.org/index.html James Altland, Oregon State Univ. North Willamette Research & Extension Center UMASS Extension @ http://www.umassgreeninfo.org/index.html Dave Powell, USDA Forest Service @ www.forestryimages.orgAngelica Table, left to right: Virginia Kline, University of Wisconsin, Madison, Dept. of Botany Flora of the Northeast United States @ www.web.syr.edu Flora of the Northeast United States @ www.web.syr.edu Albert FW Vick Jr., Native Plant Information Network @ www.wildflower2.orgPoison Hemlock Table, left to right: Dan Tenaglia @ www.missouriplants.com Dan Tenaglia @ www.missouriplants.com Patrick J. Alexander @ USDA-NRCS PLANTS Database Brother Alfred Brousseau, St. Mary's College of CA @ USDA-NRCS PLANTS DatabaseWild Parsnip Table, left to right: Linda Haugen, USDA Forest Service @ www.forestryimages.org Dan Tenaglia @ www.missouriplants.com Patrick J. Alexander @ USDA-NRCS PLANTS Database UMASS Extension @ http://www.umassgreeninfo.org/index.html